The vast majority of pancreatic ductal adenocarcinomas (PDAC) involve activating mutations in KRAS (KRAS*) and as with other KRAS* cancers, PDAC show minimal response to existing therapies used in the clinic. While no satisfactory KRAS*-speclfic drugs are currently available, inhibitors of MEK and PI3K (MEKi and PI3Ki)pathways necessary for KRAS*-mediated cellular transformation in vitro, are now being introduced into clinical trials. The central hypothesis guiding this project is that PDAC utilize the PI3K and MEK pathways In a redundant way to drive tumor growth and that a critical role for these pathways Involves the regulation of tumor metabolism. The overall goals of this proposal are to determine the impact of MEKi/PI3Ki on PDAC cell signaling, metabolism, and therapeutic response. These efforts will be coupled with an investigation of metabolic biomarkers for MEK/PI3K signaling and identification of mechanisms of therapeutic resistance which would be critical in future therapeutic trials. The Aims are: 1. Determine the impact of MEK/PI3K inhibition in PDAC. Genetically engineered mouse models as well as genomically characterized organotypic human PDAC cultures will be used to compare the cellular responses and signaling pathway alterations provoked by genetic or pharmacologic MEKi/PI3Ki against the backdrop of different combinations of tumor suppressor mutations found in human PDAC. 2. Determine the impact of MEK/PISK inhibition on PDAC metabolism. Glutamine and glucose are the main nutrients used by tumor cells for energy generation and for anabolic processes. The contribution of these nutrients to PDAC metabolism in vivo and the impact of MEKi/PI3Ki on their utilization will be determined using a series of radioisotope labeling, molecular imaging, and LC-MS approaches. These studies will give insight Into the regulation of PDAC metabolism and define biomarkers for the activity of these pathways. 3. Determine the mechanisms of resistance to MEKi/PI3Ki in PDAC. Preliminary studies indicate that mouse PDAC models will eventually develop acquired resistance to MEKi/PI3Ki. The mechanisms of acquired resistance will be explored by a series of phosphoproteomics and genetic analyses. In addition, as a means to increase the bi